1. Field of the Invention
The present invention relates to an automotive drive with a water retarder. The invention relates, in particular, to a device and a method for adjusting the optimal residual quantity of working medium in the working chamber of the retarder during non-braking operation.
2. Description of the Related Art
Retarders have been widely known in the art for a long time. Traditionally, conventional retarders have been operated with oil as the working medium. There has recently been an increasing tendency, however, to place the retarder directly in the cooling circuit of the motor vehicle and to utilize the coolant of the motor vehicle simultaneously as the working medium of the retarder. This is advantageous because it makes it possible to dispense with a separate oil circuit for operating the retarder. The heat that accumulates in the retarder can be dissipated directly via the cooling circuit of the motor vehicle.
During non-braking operation, the power loss of the retarder should be kept as low as possible. To this end, the retarder is largely emptied on shifting from braking operation to non-braking operation. Optimally, however, a predetermined residual quantity of working medium remains in the working chamber of the retarder. Up to now, it has been customary to discharge the working medium up to the predetermined residual quantity by means of the pressure produced in the retarder or, optionally, by means of additional, externally imposed pressure impulses. An absolute leak tightness of the sealing elements that seal the working chamber prevents a leakage flow into the working chamber of the retarder and, in this way, the optimal residual quantity of working medium in the working chamber is kept constant during non-braking operation.
There are several drawbacks to an absolute leak-tightness of all elements that seal the working chamber, such as the shaft seals or valves arranged in the cooling circuit that close off the branch of the cooling circuit in which the retarder is disposed from the remaining cooling circuit during non-braking operation. Extremely high-grade, precisely manufactured elements, which are expensive, can only be used. In addition, even slight wear after a short period of operation leads to the necessity of replacing these elements.
Accordingly, there is a need for a retarder that avoids the above-mentioned disadvantages of currently available systems.